Influence of olive leaf extract on the physicochemical properties of yogurts made from cow, sheep, and goat milk

This study compares the effect of OLE (olive leaf extract) on cow's, sheep's and goat's milk yogurts, in order to better understand its impact according to the type of milk used. The aim is to examine how OLE, as a source of bioactive compounds, influences yogurt properties such as antioxidant activity, and physicochemical characteristics (colour, texture, and viscosity). Each milk was enriched with OLE at 0.5%, 1%, 1.5% and 2% (w/v). The results showed a decrease in pH and an increase in acidity during storage, with no significant buffering effect of OLE for the three milk. OLE-enriched yogurts had a higher total phenol content and antioxidant activity, which increase significantly with OLE concentration. Moreover, the water-holding capacity (WHC) of the yogurts showed a tendency to increase slightly over the storage period of 14 days for cow's and sheep's milk yogurts but decreased slightly for goat's milk yogurt. Sheep's milk yogurts had the highest WHC, followed by goat's and cow's milk yogurts, indicating a better structural stability. OLE reduced brightness (L∗) and increased redness (a∗) and yellowness (b∗) for the three milks. The texture profile showed that increasing OLE concentration increased the firmness of the cow's milk yogurts, whereas the firmness of the sheep's milk yogurts decreased with storage time and OLE concentration. For goat's milk yogurt, firmness remained stable until day 7 but declined by day 14. Consequently, these results demonstrated the potential of OLE as a functional ingredient to enhance the nutritional profile and health benefits of yogurt, in particular through its antioxidant properties.